This invention relates to hydraulic axial piston pumps used to convert low pressure fluid to high pressure fluid. Such pumps use a plurality of pistons driven in axial reciprocation inside a cylinder barrel by a controlled variable angle swash plate. Under flow restricted inlet operating conditions, pumps of this type will cavitate causing noise, internal pump damage and early failure. Prior methods to prevent this phenomenon have only been partially successful, and at the expense of lower pump operating efficiency.
However, a different class of piston pumps, using slidable pistons inside a non-rotating body, incorporate check valves to separate the pumping chamber from the inlet and outlet. These pumps prevent the cavitation that has caused early pump failures. One major disadvantage of this class of pump is that the delivery rate can not be easily varied. Moreover, the control mechanism is elaborate, costly, and does not have a fast enough response time constant. Moreover, the pump is not inherently stable for operation in high-speed, high-performance, pump control systems such as for aircraft or missiles.